Picture transmission



Jan. 14, 1930. H. E. was 1,743,856

PICTURE TRANSMI SSION Original Filed Aug. 20, 1925 2 Sheets-Sheet l Jan. 14, 1930. W55 1,743,856

PICTURE TRANSMI S S I ON Original Filed Aug. 20. 1925 2 Sheets-Sheet 2 AMP Patented Jan. 14, 1930 UNITED STATES PATENT OFFICE HERBERT E. IVES, OF MONTCLAIR, NEW JERSEY,

ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N.- Y., A CORPORATION OF NEW YORK PICTURE TRANSMISSION Application filed August 20, 1925, Serial This invention relates to electro-optics and more particularly to compensating methods and devices. In a specific aspect the invention relates to a method and devices for automatically compensating for changes in the condition of a line used for propagating electro-optical images.

In a transmission system for producing images of pictures or of other objects employ- 1o ing carrier current modulated according to the characteristics of the picture. or other object, it is desirable to maintain the responsiveness of the image receiving apparatus irrespective of changes in the constants of the i5 transmission line and the associated apparatus. It is inevitable in systems requiring the use of long transmission lines that the electrical properties of these lines should vary in accordance with conditions which are not to be controlled directly, for example,changes in atmospheric conditions, temperature conditions and the like. In addition there are the variations caused by changing conditions of the electrical apparatus associated with the transmission line. The efiect of the existence of these varying conditions upon the production of images is a non-uniform reproduction of like tone values of the picture or other object. This is especially pronounced 5:0 in those systems where the picture or other object is scanned element by element and a comparatively long interval elapses between the production of the first element of the image and the production of the last element.

The present invention has for its object to provide a method and means for automatically compensating for changes in the characteristics of a transmission line leading to said terminal.

A feature of the invention relates to the means for varying the intensity of the light rays incident upon a sensitized receiving surface in accordance with the transmission characteristics of a signaling line.

if; Another feature of the invention resides in the use of carrier signaling current to actuate a transmission level compensating device.

Other features and advantages inherent in the invention while not specifically enumera) ated will be revealed by a consideration of No. 51,309. Renewed January 13, 1928.

the descriptions given hereinafter and in the appended claims.

The invention is shown as embodied in a picture transmission system similar to that disclosed in the patent of Horton et al. No. 1,606,227, issued Nov. 9, 1926. In the said system the transparent picture film is mounted upon a sending drum adapted to be rotated at a definite speed, and moved longitudinally at another speed which bears a predetermined ratio to the speed of rotation. As a result of this double motion the entire picture is scanned as a continuous line in the form of a helix. The varying transparency of the successive elemental portions of the scanned line enables corresponding quantities of light to fall upon a light sensitive cell which therefore generates a photoelectric current determined by the intensity of the incident ra s. The current from the light cell is amplified and is then caused to modulate a carrier current. which is transmitted to the receiving station. At the receiving station the incoming carrier waves are amplified and demodulate and are then impressed upon a light valve circuit to cause the reproduction of the picture upon a sensitized film. This latter film is also mounted upon a drum similar to the sending drum and is adapted to be rotated and moved longitudinally in synchronism with said sending drum. The synchronism of the sending and receiving drums is accomplished by means of a carrier current which is of a different frequency from the current carrying the picture modulations. At the receiving station the transmitted carrier currents are separated by means of appropriate filters. The term light as used herein includes not only the visible spectrum but also the radiations above and below the visible portion. The term optical alignment as applied herein to elements in the light path is intended to apply when these elements either lie in a straight line or are otherwise arranged so long as the light passes to these elements in succession. A change in direction of the light may be effected by mirrors or prisms or the like.

Referring to the drawing,

Fig. 1 shows a picture transmission system similar to that described above, utilizing a variable shutter arrangement for controlling the intensity of the light rays through the receiving light valve.

Fig. 2 shows the receiving terminal of a system similar to that of Fig. 1 with a screen of varying density for controlllng the 1ntensity of the light rays.

Fig. 3 is a modification of Fig. 2 and shows a variably operable rheostat for controlling the brilliancy of the light source.

Fig. 4 shows a picture transmitting system which is in general similar to that of Fig. 1 but with a source of picture carrier current and a separate source of carrier compensating current and also with a screen of varying density at the receiver as shown in Fig. 2.

Referring to Fig. 1 the picture 3 in the form of a transparent film is wrapped around drum 5 which is rotated and advanced longitudinally by means of the threaded shaft 6 and the threaded bearing 7. It will be noted that the picture film does not completely surround the drum 5, but is so mounted that the portion of the drum 4 between the picture edges permits covering this area with a material having uniform transparency of the proper degree to permit-uniformly exciting the cell 11 and thus cause a carrier current of the desired Value to be transmitted. This portion of the drum revolution will be designated hereinafter as the underlap period. The light from source 8 passes through an opening in the baflle plate 9 and is focused by means of lens 10 upon an elemental area of the picture. The light rays pass through the transparent film to.

effect the photoelectric cell 11 thereby producing varying picture or image current. The varying current from the cell 11 after passing though the amplifier 12 is impressed upon the modulator 13 whereby the current Waves from the oscillation source 14 are correspondingly modified. The mechanically actuated switch 18 is in the position shown in Fig. 1 when picture currents are being re ceived, and is in its alternate position during the underlap period as will be described hereinafter. I

It will also be noted that the optical system for affecting the receiving film includes a number of elements optically aligned with the source of light 21. source pass through the opening in bafiie plate 23 and then through the variable opening 24, controlled by the shutters 25 and 26. The rays are then focused by means of lens 32 upon the light valve aperture and by means of an appropriate arrangement of lenses represented symbolically by lens 33 are focused upon the receiving film mounted on drum 20. Shutter 25 is fixed while shutter 26 is capable of sliding longitudinally to vary the size-of the opening 24. \Vhen The rays from this magnet 27 is completely deenergized shutter 26 is drawn towards the right by means of retractile spring 28 to completely open the opening 24. The extension 29 is of soft iron and is adapted to be moved by means of the magnet 27 when the latter is energized. The position of shutter 26 is locked, when not undergoing adjustment, by the mechanism controlled by magnet 31, the armature of which engages the teeth in the lever 30 when said magnet is deenergized, to hold the shutter 26 in its last adjusted position. Lever 30 rotates about the point 40 when plunger 29 is moved for and is the purpose of providing finer adjustment of the movement of shutter 26. Prior to the reception of picture signals key 34 is closed and current through the winding of magnet 27, indicated by the meter in its circuit, is adjusted by means of rheostat 35 to a value corresponding to the value of current from the demodulator 17 which value is determined by the unmodulated carrier current when the line L- is in standard condition. With this standard current flow through the winding of magnet 27 the armature of magnet 31 is temporarily released by means of the operation of key 39, from engagement with shutter 26 and said shutter assumes a position which is the resultantao-f the energization of magnet 27 and the retractile force of spring 28. Key 39 is themrestored whereby the armature of magnet 31 is allowed to reengage the teeth on lever 30 controlling the shutter 26. Key 34 may now be restored but shutter 26 is held in its adjusted position by means of the armature of magnet 31. Thus by means of the tension of spring 28, a predetermined width of opening 24 may be secured corresponding to a given standard condition of line L. With the opening 24 so adjusted the receiving apparatus is in readiness to reproduce the picture.

As described in the above mentioned patent of Horton, Ives and Lgng, the sending and receiving drums are stafited in operation and rotate synchronously. The current from the carrier source 14 isthen modulated in accordance with the intensities of the successive elemental areas of the picture 3 and is impressed on line L. As noted hereinbefore, during the picture transmission period of the sending and receiving drums, switch 18 is in its normal position as shown. Accordingly, the circuit for the demodulated pictiire currents includes normal contacts of switch 18, conductors 61 and 62 and the light valve string. Under the influence of the varying picture currents, the light valve opening is changed to allow the light from source 21 to correspondingly afi'ect the sensitized receiving surface which is mounted on drum 20.

It will be noted that shaft 36 on which drum 20 is mounted carries two camming devices 19 and 37. Cam 19 is so positioned on shaft 36 that it actuates switch 18 at the beginning of the underlap period and the length of its camming surface is sufiicient to maintain switch 18 in its operated position during the complete underlap period. During the underlap period, as described in the Horton, Ives and Long patent referred to hereinabove, unmodulated carrier current is transmitted over a line L. Since switch 18 is now actuated, the current from the demodulator 17 instead of passing through the normal contacts of switch 18 passes through the alternate contact thereof over conductors 63 and 64 and through the winding of magnet 27. Under control of this current magnet 27 acts on plunger 26, but shutter 26 is held by means of the armature of magnet 31 which engages teeth in the lower edge of shutter 26. A short interval later, cam 37 operates switch contacts 38 whereby magnet 31 is energized to remove its armature from engagement with the teeth of the lever 30. Shutter 26 therefore assumes a position determined by the resultant of the attractive force of magnet 27 and the retractile effect of spring 28. Should the line L be in standard condition, the current through magnet 27 is of the same value as that which flowed through the previously adjusted resistance 35. Accordingly, under these conditions shutter 26 does not move when magnet 31 is energized. Should, however, the transmission level be ditferent from the standard causing greater or less attenuation of the received currents, then the current flowing through the winding of magnet 27 will be in proportion to the transmission level of the line L and the size of the opening 24 will bear a direct relation to the transmission level. When the underlap period is passed switch 18 is restored to normal and transfers the incoming current conductors from the winding of magnet 27 to the light valve.

From the foregoing description it will be seen that means are provided for automatically testing the strength of the current operating the light valve once during every revolution of the receiving drum, namely, during the underlap period, and for controlling in accordance with current changes the amount of light reaching the receiving film. The current changes may be due to changes in transmission characteristics of the line or to variations in terminal apparatus through which the current passes.

The two light controlling devices, the light valve having the ribbon 22 and the device having the shutters 25 and 26, are optically aligned, that is, they are so positioned that light from the source 21 passes through them in tandem and to the receiving surface on the drum 20. Their position may be such that the light path is a straight line as shown or such that the light path has a change in direction which may be effected by a mirror or prism.

Fig. 2 shows a receiving terminal similar to that disclosed in Fig. 1 but using a variable density screen 39 substituted for the shutters 25 and 26. The arrangement of earns 41 and 42 and cooperating switches 43 and 54 is identical with the corresponding cams and switches shown in Fig. 1. The screen 39 is mounted by means of arm 44 upon the moving coil 45 of the galvanometer 46. As noted in connection with the shutter arrangement of Fig. 1, prior to the reception of pictures, key 47 is operated and resistance 48 is adjusted until the current through the moving coil 45 is of a value equal to that due to the unmodulated carrier when the line is in standard condition. Key 49 is then momentarily operated to energize magnet 51. Magnet 51 withdraws its armature from engagement with the teeth on the edge of screen 3 The screen therefore assumes a position determined by the current flowing through the resistance 48. Key 49 is then released causing the armature of magnet 51 to reengage the teeth on the screen to hold the same in its adjusted position corresponding to a standard transmission level of the line until the reception of picture currents. During the picture transmission period of the receiving drum, the switches 43 and 54 are in their normal position as shown.- Accordingly, the incoming picture currents pass through the normal contacts of key '54 and through the light valve string. The opening of the light valve is therefore changed in accordance with the received picture currents and the intensity of the light incident upon the receiving film is determined by the density of that portion of the screen 39 which intercepts the light from the source 52. During the underlap period of the receiving drum, switch 54 is actuated and transfers the incoming current leads from the light valve to the moving coil 45. An instant later, cam 41 operates switch contacts 43 whereby magnet 51 is energized and withdraws its armature from engagement with the screen teeth. Screen 39 therefore assumes a position which is determined by the transmission level of line L. disengages its corresponding switch contacts, the armature of magnet 51 is released and holds the screen 39 in its adjusted position. It is to be observed that the amount of light passing through screen changes inversely as the changes in transmission. If the transmission level is lowered a more transparent portion of screen 39 is interposed by means of galvanometer 46 between the light source 52 and the light valve, and vice versa.

Fig. 3 shows transmission level control apparatus at a receiving terminal similar to that disclosed in Figs. 1 and 2. In this case, however, the unmodulated carrier current which is sent during the underlap period inlVhen cam 41 I lee stead of controlling the action of a light intercepting device controls directly the brilhancy of the light source by means of a variablyoperable rheostat which is connected in series therewith. The sequence of operations in this case is similar to that described in connection with Figs. 1 and 2. During the underlap period, cam 71 operates switch 74 and the unmodulated carrier current is applied to the winding of magnet 75. It Will be noted that the position of .the rheostat arm 76 corresponding to a standard transmission level is adjusted in a similar manner to that already described by means of keys 77 and 78 and the variable resistance 79. Magnet 75 when energized by the demodulated carrier current during the underlap period attracts the soft iron portion 80 which is attached to the rheostat operating arm 81, causing this arm to vary the resistance in series with lamp 82 when the transmission level varies from the stamlard. It is believed that in view of'the descriptions given in connection with Figs. 1 be necessary.

Fig. 4 shows a picture transmission system utilizing a source of oscillations for the picture carrier current and a separate source of oscillations for. the compensating current. At the receiving station. there is provided an optical system similar to that disclosed in Fig. 2. The light incident upon the photoelectric cell 90, after passing through the transparency of the film, is impressed upon the picture amplifier 91. The output of amplifier 91, by means of the modulating device 92. correspondingly changes the amplitude of the carrier waves generated by oscillator 93. The modulated waves are then impressed upon the transmission line L after passing through the terminal amplier 94. At the same time, a compensating carrier current of constant amplitude generated by the oscillator 95 passes through the terminal amplifier 96 and is impressed upon the line L simultaneously with the impression of the picture carrier current. At the receiving termiand 2, further description of Fig. 3 will not nal as shown in the right of Fig. 4, the pic ture and compensating carrier currents are separated by their respective filters 97 and 100. The current passing through filter 97 is impressed upon the amplifier 98 and is demodulated by the device 99 to control the amount of current flowing through the light valve 109 as described in the Horton, Ives and Long patent referred to hereinbefore. The compensating carrier current which passesthroughfilter100is impressed upon the amplifier 101 and is demodulated by the device 102. The output of the demodulator 102 is connected by means of conductors 103 and 104 to the winding of the moving coil 105 of the galvanometer 106. The variable density screen 107 which is mounted by means of arm 108 on the moving coil 105 assumes a position transmission line characterstics. ly, changes 1n the line characteristlcs are au-.

determined by the output of the demodulator 102. Thus, it will be seen that screen 107 assumes a. position which is a function of the Accordingtomatically compensated for at the receiving terminal.

What is claimed is:

1. The method of maintaining uniform reception in a s stem for producing images of pictures or 0 other objects of the type em ploying a. light beam to produce the image which comprises acting on the light beam directed to a receiving surface in accordance with changes in the transmission level of a line and independently of the picture currents being received and their control of the light beam.

2. In a system for producing images of pietures or of other objects, a sending station, a receiving station, a transmission line for interconnecting said stations,means for sending image currents over said line, means for sending test currents over said line, a light compensating device at the receiving station and means responsive to the sending of said test currents only to cause said light compensating device to maintain uniform contrast relation between the image and the object.

3. In a system for producing images of pietures or of other objects, a sending station, a receiving station, a transmission line for interconnecting said stations, means for sending over said line currents modulated in accordance with the tone characteristics of a picture or object, means for receiving said currents, a source of light and a receiving surface therefor at the receiving station, a device at the receiving station adapteid to control the amount of light reaching said surface, means for receiving testing current dependent upon the condition of said line, and means responsive solely to said test current for correspondingly varying the intensity of the light from said source.

4. In a system for producing images of pietures or of other objects, a sending station, a receiving station, a transmission line for interconnecting said stations, a receiving surface and a source of light therefor at said receiving station, means for transmitting a carrier current modulated according to the tone characteristics of a picture or other object from said sending station to said receiving station, means for sending unmodulated carrier current to test said line, means at said receiving station for varying the intensity of the light rays from said source in accordance with the modulated currents, and optical means at said receiving station for varying the intensity of the light from said source in accordance with said test.

5. The combination in a system for pro ducing images of pictures or of other objects of a transmlssion line, a receivmg surface and a source of light therefor, a light valve actuated by image currents received over said line to correspondingly control the intensity of the light from said source, a variable density screen and means responsive to changes in the characteristics of said line for moving said screen to correspondingly control the intensity of the light from said source.

6. The combination in a transmission system for producing images of pictures or of other objects of a line, a receiving surface and a source of light therefor, means comprising a screen for varying the intensity of the light reaching said surface directly as the currents received over said line, and means for varying the intensity of the light reaching said surface inversely as the currents received over said line.

7. The combination in a transmission system for producing images of pictures or other objects of a sending stat-ion, a receiving station, a line connecting said stations, means at said sending station for generating a carrier current, a light valve, a light screening device at said receiving station, means for applying said current to said line to control said valve, and means at said receiving station for periodically switching said current from said valve to said device.

8. In a transmission system for producing images of pictures or of other objects, a sending station, a receiving station, a line for interconnecting said stations, means at the sending station for testing successive elemental areas of a picture to be transmitted, means for generating image currents corresponding to the characteristics of said tested areas, a source of carrier current, means for modulating said carrier current by said image currents, a receiving station and a receiving surface thereat, a light valve and a light compensating device at said receiving station, means for adjusting said device to correspond to a standard condition of said line, means at said receiving station for receiving said carrier current, means for applying the modulated carrier currents to the light valve to correspondingly control the intensity of light incident upon said surface, and means for applying the unmodulated carrier current to said device to compensate for varying conditions of said line.

9. In a transmission system for producing images of pictures or of other objects, a sig naling line, a receiving surface, a source of light therefor, a light valve responsive to impulses over said' line to control the intensity of light upon the surface, a variable density screen, and means responsive to changes in transmission levels of the signaling line for moving said variable density screen to further control the intensity of light from the source.

10. In an electro-optical image producing system, a source of light and a plurality of light valves for variably and successively acting upon light from said source.

11. In an electro-optical system, a transmission line, a light valve, means for pcriodically locking and releasing said light valve, and means for periodically controlling the light controlling power of said valve when in release condition in accordance with a transmission characteristic of said line.

12. In an electro-optical receiving system, a source of light, and a plurality of electrically controlled light valve acting on the same beam of light from the said source and cont-rolled by incoming currents.

13. An electro-optical signaling system, comprising at a. receiving station a source of light, and a plurality of light valves acting on the same beam of light from the said source, and means at a transmitting station for controlling said valves.

14. In an electro-optical system, a. source of light, and two light valves intercurrently actuated to vary the same beam of light from the said source.

15. In an electro-optical system comprising a source of light and a light valve limiting the total amount of light transmitted in a given direction from said source, means for operating said light valve only during the underlap period and a second light valve cooperatively inoperative during the said period.

16. In an electro-optical system compri ing a source of light and two light valves, means for rendering one of said light valves inoperative during the underlap period.

17. An electro-optical system for producing images of pictures or of other objects. comprising a light valve operated by current transmitted over the line transmitting image current but operating independently of said image current, and automatic means for alternately locking and relesaing said valve.

18. In an electro-optical system, a source of light, a plurality of light valves optically aligned with said source, each of said valves having a light transmitting channel of variable transmitting power, and means for causing said transmitting power of the different valves to vary at difi'ercnt rates.

In witness whereof, I hereunto subscribe my name this 15th day of August A. D.. 1925.

HERBERT E. IVES. 

